Hydrofoil boat



United States Patent 3,l5,495 HYDROFGIL BOAT @sear Erlandsen, Garden(Iity, N.Y., assignor to Thurston Erlandsen Qorporation, Sanford, Maine,a corporatien of Maine Filed Mar. 13, N63, Ser. No. 264358 3 Claims.(Cl. 114-665) This invention relates to new and useful improvements inhydrofoil design and more particularly seeks to provide a variable sweeparrangement of the hydrofoils for waterborne vehicles.

Stationary hydrofoils, to some extent, limit the efficiency of ahydrofoil boat by limiting its maximum efficiency over a wide speedrange. If the stationary hydrofoils are generally transverse to thehull, there will be a relative high drag at high speeds, whereas if thestationary hydrofoils are swept back, there will be relatively smalllift at low speeds. Hence, there is no one ideal planform or positionfor the hydrofoils of a high speed ratio (wide range) vehicle andoperating efliciency is consequently lost at certain speeds in ahydrofoil boat having fixed planform hydrofoils.

It is, therefore, amongst the primary objects of the present inventionto increase the efficiency of hydrofoil boats by varying the planform orposition of the hydrofoils at varying speeds.

It is another important object of the present invention to enlarge theeflicient operational speed range of a water-borne vehicle by hydrofoilmodification.

It is still another important object of the present invention to providea water-borne vehicle having movable hydrofoils so that the same may beswept back at high speeds, extended transversely at low speeds and madeto assume a variety of intermediate positions in order to have the bestsweep angle at intermediate speeds for maximum operational efficiency.

With these and other objects and features in mind, the nature of whichwill be more apparent, the invention will be more fully understood byreference to the drawings, the accompanying detailed description and theappended claims.

In the drawings:

FIG. 1 is a diagrammatic plan view of a variable sweep hydrofoil inaccordance with the present invention;

FIG. 2 is a diagrammatic vertical section through a boat equipped withthe hydrofoils of FIG. 1; and

FIG. 3 is a graph plotting L/D in air (equivalent to lift over drag)against Mach number (speed) and Reynolds number with NACA foil 0012,chord1'=0", and C =0.4.

This invention, as illustrated, discloses a hydrofoil system mountedunderneath a conventional hull l8, hydrofoils and 12 being mounted inhousing 11 to pivot about points 14 and 16, respectively, as shownschematically in the drawings. The housing ll. is attached to and spacedfrom the hull by struts 9. The foils l0, l2. and the housing 11 arefoil-shaped in cross-section to provide lift via well known hydrodynamicprinciples.

By reason of the foregoing construction, said hydrofoils may be made toassume a swept back position, a position which is most advantageous athigh speeds. If the hydrofoils operate in the same plane, a portion ofthe base end of each hydrofoil may be arranged angularly of theremainder, as at 25 and 28, so they will not 0'0- 3,195,495 PatentedJuly 20, 1965 struct each other when assuming the swept back position.The angle of sweep is shown at transverse to 45 behind transverse; butgenerally may be between about 10 in front to behind transverse,transverse being measured from the longitudinal axis of the hull. Foilit; (and dotted 3.2) is shown in slow transverse position, whereas 12 isshown in fast swept back position, although in operation, both would bein the same relative position.

At low speeds the same hydrofoils may readily be extended transverselyof the hull to again assume a most advantageous lift position. Forintermediate speeds, intermediate positions may be selected for saidhydrofoils.

As will be seen from FIG. 3, the drag on an unswept airfoil of theparticular design is constantly less on an unswept Wing up to about 0.6Mach with the difference decreasing until they cross at about 0.63.However, on reaching 0.8 Mach, the drag on the unswept wing is more thandouble the 35 swept wing.

Since the basic principles of the dynamic forces eX- erted by a fluid ona foil moving therein are applicable to both air and water, both beingfluids, the airfoil theory with proper adjustments, is applicable tohydrofoils.

The proportions, plus mechanical and structural considerations of theairplane wing render the overall advantage of the variable sweep wing asa dubious quantity in most cases. However, the hydrofoil wing isgenerally smaller, more compact and more heavily loaded than theairplane wing and, therefore, the structural, mechanical and weightpenalties involved in introducing variable sweep are less critical forthe hydrofoil boat. Thus, to take full advantage of minimum possibledrag for a given lift, as applied to a high performance (i.e., widerange) boat, it is necessary to have a variable sweep wing.

The motive power for pivoting the hydrofoils may be derived from thepower plant of the water-borne vehicle or from an independent powersource, e.g. electrical or hydraulic. if the power plant of the vehicleis to be utilized, the hydrofoils may be readily linked by suitablegearing to the drive shaft for the boat propeller. They may, of course,be driven by conventional propeller, jet power, or other suitablepropulsion means.

By providing a suitable system of gearing and clutches, the rotationalmoment of the drive shaft may be translated with minimum energy lossinto the reversible linear movement required for the above describedvariations in hydrofoil position. An arrangement for locking thehydrofoils in any of the various possible positions therefor may readilyand economically be combined with such gearing and clutches.

It may be seen from FIG. 3 that the optimum sweep angle of a particularhydrofoil is a function of the hydrofoil speed and other considerations.Hence, control of the sweep angle may be made automatic and as afunction of hydrofoil speed. On the other hand, control may resideexclusively in the pilot and, of course, a dual system of controls maybe provided.

Although the invention has been described in detail with respect to onepreferred embodiment thereof, it will be understood by those skilled inthe art, after reading this specification, that various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

I claim:

1. In a water borne vehicle including a hull and a hydrofoil havingcontinuous leading and trailing edges extending generally transverse tothe longitudinalaxis of i through a variable sweep back angle Withoutbraking the continuity of said leading and trailing edges whereby theplan view of said hydrofoil is continually changed with said pivoting. pI

' 2. he vehicle of claim 1 wherein said side sections are pivoted abouta point on the proximal end thereof 7 positioned Within'the plan of saidmid-section in such a manner that the saidleading and trailingledges ofsaid ,side sections are always partly Within the plan of saidamid-section.- I a 7 1 3. The vehicle of claim 1 wherein said pivotalangles of said side sections are between about 10 forward to 85 rearwardof transverse, transverse being 90 from the longitudinal axis.

V ReEerences Cited by the Examiner V UNITED STATES PATENTS FERGUS' 's,MIDDLETON; Bi'iprary Examiner;

1. IN A WATER BORNE VEHICLE INCLUDING A HULL AND A HYDROFOIL HAVINGCONTINUOUS LEADING AND TRAILING EDGES EXTENDING GENERALLY TRANSVERSE TOTHE LONGITUDINAL AXIS OF SAID HULL, THE IMPROVEMENT IN COMBINATIONTHEREWITH WHEREIN SAID HYDROFOIL INCLUDES A STATIONARY MID-SECTION AND ASECTION ON EACH SIDE OF SAID STATIONARY SECTION, AND FURTHER COMPRISINGMEANS TO PIVOT EACH SIDE SECTION THROUGH A VARIABLE SWEEP BACK ANGLEWITHOUT BRAKING THE CONTINUITY OF SAID LEADING AND TRAILING EDGESWHEREBY THE PLAN VIEW OF SAID HYDROFOIL IS CONTINUALLY CHANGED WITH SAIDPIVOTING.